Dispatching presence events for all users in a workspace is an expensive operation for Slack. A flood of presence events from large workspaces can also disrupt your app's ability to process more useful, timely messages.

By subscribing only to the presence events your app needs to provide presence-dependent functionality, you can reduce unnecessary websocket traffic.

In addition, rtm.start will no longer include user presence and online field information in its initial preamble JSON. You'll need to use users.getPresence to determine initial presence status instead.

What isn't changing?

Presence events are not currently issued as part of the Events API, therefore nothing is changing on the Events API.

What happens if I do nothing?

Your app will stop receiving presence_change events on any websockets your app is connected to beginning November 15, 2017. If your app uses those presence events to direct functionality, your app might not do what it's supposed to do without that information.

Your app will no longer receive the current state of presence and online information for workspace users when connecting via rtm.start.